Quinolone resistance in Pseudomonas aeruginosa and Staphylococcus aureus. Development during therapy and clinical significance.

This review focuses on published information on the experimental as well as clinical data on the emergence of quinolone resistant isolates. In the course of clinical use of fluoroquinolones, only a sporadic emergence of quinolone resistance has been noted. The resistant organisms emerged particularly in certain clinical settings where large numbers of organisms frequently causing chronic infections are present and/or in loci where quinolone concentrations may not be optimal. In terms of occurrence in individuals, quinolone resistance has emerged most frequently in hospitalized and nursing-home patients with identifiable risk factors. Epidemiological studies revealed that in nearly all the cases studied one or one predominating quinolone resistant clone was selected that was horizontally transmitted. Thus, the emergence of quinolone resistance is not due to an independent selection of resistant strains in a number of patients, but to the clonal spread of one strain once it has acquired quinolone resistance. Therefore, the rate of quinolone resistance is very likely to be lower than reported.